In areas where heavy current is supplied to the buildings through direct current mains, elevator drive systems are naturally based on the use of direct current and, almost always, direct current motors. In such areas, e.g. in New York City, besides the direct current supply, there is usually a 220 V a.c. supply available for lighting purposes. Where direct current is the chief energy form, modern a.c. converters cannot be used. Under these circumstances there are considerably fewer alternatives for elevator motor drives, and modernization of existing drives--most commonly dynamic Ward-Leonard converters--is often seen as a more rational solution than complete renewal.